This proposal presents an approach to the study of the regulation of the humoral immune response at the level of individual T and B lymphocytes. The regulation of antibody responses appears to be a complex biological phenomenon which is mediated, in part, by the cells of the immune system. The mechanisms which serve to regulate antibody synthesis are not, at this time, well understood. Hopefully, a better understanding of the mechanisms by which immune responses are controlled can be gained through an investigation of the characteristics and interaction of individual B and T lymphocytes which participate in antibody responses. Techniques have been established which allow for the isolation and antigenic stimulation of individual B and T lymphocytes. Such techniques have been particularly successful in studying the regulation of B cell antibody responses in the past as these methods allow one to independently assess several aspects of the B cell's antibody response to antigen. These techniques will be employed to study: 1) The requisites of antigenic stimulation of individual B cells or more generally B cells of a defined subpopulation, 2) the conditions which govern the appearance of B-cell subpopulations, 3) the factors which govern T-cell interactions with B cells of different subpopulations and the manner in which these interactions serve to specifically regulate B-cell responses, 4) the diversity of the T-cell repertoire available for participation in B-cell antibody responses, 5) the functional capacity of individual T cells in collaborative or suppressive interactions with B cells, 6) the mechanisms (T or B cell dependent) which function to regulate antibody responses once initiated.